Aqueous coating materials comprising at least one ionically and/or nonionically stabilized polyurethane which is saturated, unsaturated and/or grafted with olefinically unsaturated compounds are known. They may be cured physically, thermally, or both thermally and with actinic radiation. Preferably they comprise color and/or effect pigments and are used for producing color and/or effect paint systems, especially basecoats as part of multicoat paint systems, or solid-color topcoats.
The known aqueous coating materials may comprise organic solvents, especially high-boiling (“long”) organic solvents, such as heterocyclic, aliphatic or aromatic hydrocarbons, mono- or polyhydric alcohols, ethers, esters, and ketones, such as N-methylpyrrolidone, toluene, xylene, butanol, ethylene glycol and butyl glycol and their acetates, butyl diglycol, ethylene glycol dibutyl ether, diethylene glycol dibutyl ether, ethoxypropanol, cyclohexanone, methyl ethyl ketone, acetone or isophorone (cf. European patent applications EP 0 228 003 A1 and EP 0 634 431 A1).
Among these solvents, N-methylpyrrolidone in particular effectively prevents the formation of spray mist bittiness.
From German patent DE 100 43 405 C1 it is known to add triorganophosphates, particularly trialkyl and/or tricycloalkyl phosphates such as tripropyl, tributyl, triamyl, trihexyl or tricyclohexyl phosphate, to the aqueous coating materials in order to increase the water-vapor permeability of the applied coating materials and to lessen their tendency to form pops and pinholes.
Among these triorganophosphates, tributyl phosphate has proven particularly effective.
Nevertheless, in practice, N-methylpyrrolidone and tributyl phosphate give rise to toxicological problems, and so attempts are being made to replace them by compounds at least as effective if not, indeed, more effective, but free of such toxicological problems.